1. Field of the Invention
The present invention relates to a chemical sensor using metal nano-particles and a method for manufacturing a chemical sensor using metal nano-particles and, more particularly, to a chemical sensor using metal nano-particles having excellent detection characteristics and durability, and a method for manufacturing a chemical sensor using metal nano-particles.
2. Description of the Related Art
A typical chemical sensor is a metal oxide sensor, which performs sensing (or detection) at a high temperature (200 degrees Celsius to 400 degrees Celsius). Specifically, as metal oxide of a surface of the metal oxide sensor is activated at a high temperature, an oxidation-reduction reaction takes place between the metal oxide on the surface of the metal oxide sensor and target molecules to be sensed, thus performing sensing. Because the oxidation-reduction reaction irreversibly occurs, the activity of the surface degrades over time to end in a loss of the sensing function.
Thus, the service life of the metal oxide sensor is not long, and a correction function with respect to a change in sensing characteristics of the metal oxide sensor is performed even during the service life period. For all these drawbacks, metal oxide type sensors make up the majority of commercial sensors: The reason for this is because metal oxide has solidity or firmness in detection performance and chemical sensors have advanced in line with a great deal of commercialization efforts based on metal oxide playing a key role.
In order to overcome the inconvenience of high temperature detection, a sensor using a polymer detection film has been developed. This sensor includes a polymer as a detection film on an electrode. Detection is performed such that the polymer film absorbs a target material to be analyzed in the air and the mechanical or electrical characteristics of the polymer are affected by the amount of the absorbed target material, thus performing sensing.
A sufficient amount of sensing may take place at room temperature, so that sensing is performed at room temperature. A sensing reaction time relies on the dynamic equilibrium of the target molecules to be sensed on the surface of the polymer, and in general, the dynamic equilibrium on the surface of the polymer takes a long time.
There has been a case in which gold nano-particles surrounded with octanethiol were present in the form of a thin film on an electrode substrate, which was used as a chemical sensor. In this case, an excellent sensitivity for a level of 1 ppm of toluene was obtained, and a reaction time was a few seconds.
However, although the octanethiol gold nano-particle sensor exhibited excellent sensitivity for non-polar molecules, this was not the case for alcohol or water, both of which are polar sensing targets.
In another case, a layer of gold nano-particles surrounded with phenol was synthesized to implement a chemical sensor in the form of a thin film on an electrode substrate, which had good sensitivity for polar molecules. In particular, the chemical sensor is able to detect moisture even at a tens of ppm level.
However, even the lapse of scores of minutes at a 100 ppm degree did not reach saturation, indicating that the reaction was still going on. Namely, although the sensitivity for the polar molecules was excellent, the reaction time took too long.
In addition, the morphology of the sensor thin film of the chemical sensor using a polymer or metal nano-particles may change over time. In particular, a physical structure maintained by the sensor thin film may change according to an interaction between gas molecules and the sensor thin film, while reacting to various types of vapors, to result in a change in the sensing characteristics.
That is, unlike the metal oxide sensor, the chemical sensor does not involve a chemical irreversible reaction, so its sensing performance is not degraded over time, but the change in the physical structural characteristics of the sensor thin film as mentioned above is likely to degrade the reliability of the sensing operation of the chemical sensor.